In accordance with the present invention a compact high fidelity sound reproduction system is provided which is characterized by high efficiency, low distortion, wide bandwidth, and extended low frequency reach. The sound reproduction system or speaker can be used as a sub-bass woofer, bass woofer, mid-bass woofer, and mid-range speaker. Moreover, it can be used to achieve these range categories alone or in combination. Certain embodiments can even be effectively used over an octave range that spans at least, and even more than seven octaves, i.e., from 20 Hz to 1.5 kHz, with a single or multiple dynamic driver(s) and excellent acoustic efficiency (e.g., the present embodiment achieves 98 dB(C) (decibels, C-weighted) at 1 meter and 2.83 volts) and high fidelity performance (e.g., the present embodiment achieves a total harmonic distortion (THD) of <0.4% at 50 Hz, and 100 dB(C) sound pressure level (SPL) at 1 meter). The speaker of the present invention is particularly advantageous for use in public announcement type settings which cover large or open areas, although private acoustic enthusiasts could find use for the invention in part because of its relative small size (it is easily transported as it can be made having a small footprint, for example having a volume of less than two cubic feet and a weight of less than 30, or even 20 pounds), its efficient energy consumption, and suitability for use in public or private locations, including both commercial and residential applications. The new speaker technology presented here is a completely new alignment unlike any previous speaker topology (as evidenced by the unique electrical impedance plot containing at least 5 peaks).
In the past, sound reproduction systems have provided speakers using various means to achieve sound reinforcement systems or for stage performance systems for projection over large distances or in large spaces such as arenas and stadiums, but these have fallen short in one or more of the desired range of reproduction, the acoustic efficiency, the high fidelity performance, or the size of the device. The present invention addresses these and other objectives. It can be used for various media events that require sound reproduction or amplification, including for example, public speaking addresses; orchestral, dance and theatrical performances; rock, jazz or pop concerts; movie, surround sound or amusement park type experiences; places of worship; arena events such as sporting or skating; school presentations; and high fidelity home audio and home theater experiences; to name a few.
Some of the means which attempted to achieve these objectives presented by the prior art include (1) bass horns where the front of the driver cone is coupled to a front facing horn in the direction of sound propagation, and the rear of the driver cone is coupled to a sealed back cavity used to control the motion of the cone in order to maximize the SPL by limiting cone motion; (2) tapped horns where the front and rear side of a driver diaphragm are in communication through a common horn passage which is used to enhance the efficiency while keeping the horn size compact; (3) bass reflex speakers where a rear chamber is connected to the outside through a tuned duct in order to lower the system's resonant frequency; (4) transmission line speakers whereby the front or rear of a driver is in communication with a long duct that is open on the distal end so that it provides gain for the back wave from a driver cone; (5) mass-loaded transmission line, whereby a constricted duct is connected to the outside and serves to lower the resonant frequency of the TL; (6) back loaded horns where the backside of the driver cone is in communication with an expanding horn that serves to provide gain for the lower bass frequencies; (7) bandpass enclosures where the driver is enclosed within several chambers connected by ducts that serve to provide gain for lower bass frequencies through the tuning of multiple resonant chambers, one of which encloses the front face of the driver and another chamber which encloses the rear of the driver; or (8) so-called Karlson type bandpass enclosures where a curved aperture placed over the acoustic outlet serves to provide a dimensionally non-discrete mouth element so that resonant horn-induced peaks are reduced; and (9) a sealed chamber enclosure where the back cone volume is enclosed by a sealed box filled with acoustically absorbent material such as fiberglass, foam, or other fibrous material to absorb the back wave acoustic radiation.
The prior art systems all have a significant limitation in bandwidth of operation and are typically no wider than about 2 octaves (e.g., 20 Hz to 80 Hz, or 40 Hz to 160 Hz). Bass horns must be physically large in order to achieve bass extensions that reach 40 Hz due to the speed of sound and the required ¼-wave length of the fundamental frequency of the lowest note desired. In the case of 20 Hz, the nominal length of a bass horn is over 4.2 meters. This length coupled with a typical desired expansion ration of 1:10 will cause the resulting enclosure (even with folded passage ways) to be quite large for a bass woofer driver in the nominal 12-inch driver size. Another significant disadvantage of the prior art is that the large cone motions often cause higher harmonic distortion (as much as 10% to 30% THD). Such distortions make the bass notes sound ‘muddy’ or indistinct. Other disadvantages of prior art such as a bass reflex enclosure are significant delays in the arrival time of the sound as a function of frequency. This shows up as curves and peaks in an impulse response plot that is indicative of the timing (or phase distortion) that is produced by the speaker.